Conventionally, as bearings usable with a long period of greasing interval or without greasing, oil-containing slip bearings prepared by allowing pores in a Cu-based or Fe-based porous sintered alloy to contain a lubricating oil are widely put into practical use. Selection of the Cu-based or Fe-based porous sintered alloy is determined depending on conditions such as oil lubricating state, sliding speed, contact surface-pressure and the like, and under light-load and high-speed sliding conditions, a bronze-based oil-containing slip bearing is suitably utilized, whereas under high-surface-pressure and low-speed sliding conditions, a Fe—C, Fe—Cu or Fe—C—Cu-based oil-containing slip bearing is suitably utilized (see, for example, Japan Powder Metallurgy Association ed. Parts—Their design and manufacture”, Gijutsu Shoin Co., Ltd., Oct. 20, 1987, p. 327-341). On one hand, there are widely utilized also slip bearings produced by orderly arranging graphite fragments as a solid lubricant on a bearing material made of high tensile brass and bronze, and allowing the graphite fragments to contain a lubricating oil (for example, 500 SP manufactured by Oiles Corp.). On the other hand, prior technologies aiming at improvement in a sliding property under high surface pressure and low speed sliding are shown in the following various patent literatures.
Japanese Patent No. 2832800 adopts a composite sintered alloy having a porosity of 5 to 30 vol % and composed of a copper powder and an iron powder, as an iron-based sintered body in a slip bearing in which a lubricating oil having a kinematic viscosity of 240 cSt to 1500 cSt is impregnated on an iron-based sintered body oil-containing bearing used under sliding conditions of a high surface pressure of 600 kgf/cm2 or more and a sliding speed of 1.2 to 3 m/min, and discloses that it is preferable to perform a carburizing, nitriding or sulfurizing nitriding treatment on a contact surface.
Japanese Patent Application Laid-Open (JP-A) No. 10-246230 discloses that a slip bearing produced by filling a lubricant composition containing a solid lubricant or an extreme-pressure additive having a dropping point of 60° C. or more in semi-solid condition or solid condition at ambient temperature, into pores in an iron-based sintered alloy containing martensite in an iron-carbon alloy base and in which at least one of copper particles and copper alloy particles are dispersed, shows excellent slip bearing performance under a surface pressure of 30 MPa or more.
Japanese Patent Publication (JP-B) No. 6-6725 discloses that a sintered copper alloy having self lubricity suitable for use on a ware plate of a press machine and the like is obtained by sintering under pressure a mixed powder prepared by mixing a copper alloy powder containing 5 to 30 wt % of Ni, 7 to 13 wt % of Sn and 0.3 to 2wt % of P with 1 to 5 wt % of Mo and 1 to 2.5 wt % of a graphite powder.
JP-A No. 8-109450 discloses a wear resistant sintered alloy for oil-containing bearing characterized in that Cu particles or Cu alloy particles are dispersed in an iron-carbon alloy base having martensite present therein, the content of Cu is from 7 to 30 wt % and, alloy particles having a specific composition as a phase harder than the above-mentioned iron-carbon alloy base are dispersed in an amount of 5 to 30 wt % and the porosity is from 8 to 30 vol %. In this wear resistant sintered alloy for oil-containing bearing, by dispersing a large amount of soft Cu particles in a martensite phase, conformability is improved, and by dispersing alloy particles harder than the martensite of the base, plastic deformation of the base is decreased and load applied on the base alloy in sliding contact state is lowered, to obtain excellent wear resistance even under high surface pressure. Here, this patent literature mentions, as the above-mentioned alloy particles, {circle around (1)} Fe-base alloy particles (high speed steel (Highss) powder particles) containing 0.6 to 1.7 wt % of C, 3 to 5 wt % of Cr, 1 to 20 wt % of W and 0.5 to 6 wt % of V, {circle around (2)} Fe-base alloy particles (high speed steel (Highss containing Mo, Co) powder particles) containing 0.6 to 1.7 wt % of C, 3 to 5 wt % of Cr, 1 to 20 wt % of W, 0.5 to 6 wt % of V and 20 wt % or less of Mo and/or Co, {circle around (3)} Mo—Fe particles (ferro-molybdenum) containing 55 to 70 wt % of Mo, {circle around (4)} Co-base alloy particles (heat resistant and wear resistant alloy powder for build up spraying, trade name: COBAMET manufactured by Cabot) containing 5 to 15 wt % of Cr, 20 to 40 wt % of Mo and 1 to 5 wt % of Si; and the like.
JP-A No. 2001-271129 which is a prior application of the applicant discloses a slip bearing characterized in that hard dispersion materials such as various intermetallic compounds and the like, solid lubricants such as graphite and the like may be contained in an (alpha+beta) two-phase structure having at least a beta phase dispersed in the structure, or a beta phase structure constituting a Cu—Al—Sn-based sintered contact material, and in which, further, the Cu—Al—Sn-based sintered contact material is integrated on the inner circumferential surface of an iron-based backing metal, so as to maintain bearing rigidity and press fit force in press-fitting on a work implement connecting apparatus. In this slip bearing, the above-mentioned Cu—Al—Sn-based sintered contact material is soft as compared with the bearing material containing martensite according to the above-mentioned patent literature 4, and excellent in conformability with a contact opposite member (work implement connecting pin or the like). Therefore, this sliding bearing is an extremely excellent sliding bearing which can be suitably used at extremely low sliding speed (0.6 m/min or less) and a high surface pressure of up to 1200 kgf/cm2.
JP-A No. 7-166278 discloses that a sintered contact material having an excellent lubricating ability, affinity to oil, low friction coefficient and high wear resistance can be obtained by adding 0.5 to 5 wt % of Mo or 0.5 to 15 wt % of Fe—Mo into a bronze-based and/or lead bronze-based sintered contact material containing 4 to 12 wt % of Sn or this and 0.1 to 10 wt % of Pb.
On one hand, comparatively soft lead bronze ingot materials (for example, LBC 2 to 5) are often used as, for example, a contact material for floating bushing of a turbo charger used under high speed, high temperature and oil lubrication conditions, however, from the standpoint of corrosion resistance under high temperature sliding condition (sulfur attack property), free-cutting brass-based and high tensile brass-based alloys containing Pb are suitably used (see, for example, JP-B No. 5-36486). Additionally, Al bronze-based ingot materials are also investigated as the contact material for floating bushing (see, for example, JP-A No. 5-214468).
On the other hand, in the case of, for example, engine metals used under high surface pressure and high speed sliding conditions, an overlay layer made of a soft metal such as Sn and the like is formed on a contact surface of a lead bronze-based sintered bushing to improve conformability and to obtain improved fluid lubricity.
Further, in parts sliding under high surface pressure and high speed conditions (hereinafter, referred to as “sliding part”) of constituent parts of hydraulic pumps/motors used under high surface pressure and high speed sliding conditions likewise, a material containing lead bronze integrated by a cast wrapping method and the like is used as a constituent material, and in sliding parts used under particularly severe sliding conditions, materials having high strength, and excellent seirzure resistance and wear resistance such as high tensile brass are used as a constituent material (see, for example, Japan Non-ferrous Metal Casting Association ed., “ENGINEERING DATA BOOK FOR COPPER BASED ALLOY CASTING ”, Issued by Materials Process Technology Center (SOKEIZAI CENTER), Jul. 30, 1988, p. 134-155).
In general, it is extremely rare to attain fluid lubricating condition on an oil-containing slip bearing, and particularly under extremely low sliding speed and high surface pressure conditions, the film thickness of a lubricant oil on a bearing surface (contact surface) becomes, due to escape of oil pressure through pores in a sintered material, approximately the surface roughness of the bearing surface or smaller, and in many cases, boundary lubricating sliding conditions including solid friction (adhesion) are provided. Consequently, in slip bearings (bushing, thrust bearings and the like) used under sliding conditions of a surface pressure of 300 kgf/cm2 or more and a sliding speed of 0.01 to 2 m/min, in a work implement connecting portion of construction machines such as, for example, a hydraulic excavator and the like, its seizure resistance and wear resistance are significantly ruled by material functions of the sliding bearing (composition and structure).
However, the Cu-based and Fe-based porous sintered alloy material according the above-mentioned literature (Japan Powder Metallurgy Association ed. “P/M Parts—Their design and manufacture”, Gijutsu Shoin Co., Ltd., Oct. 20, 1987, p. 327-341) has a problem that it cannot be adapted to extremely low sliding speed and high surface pressure conditions of a sliding speed of 0.01 to 2 m/min and a surface pressure of 300 kgf/cm2 or more, as apparent from FIG. 21 showing the application range of an oil-containing slip bearing generally used (Japan Powder Metallurgy Association ed. “P/M Parts—Their design and manufacture”, Gijutsu Shoin Co., Ltd., Oct. 20, 1987, p. 337, FIG. 6. 19 “Sintered bearing application example”, is cited).
Even a composite sintered alloy material according to Japanese Patent No. 2832800 in which surface treatments such as carburization, nitriding and the like are performed on a composite sintered alloy composed of a copper powder and an iron powder, and an iron-base sintered alloy material according to JP-A No. 10-246230 in which pores are filled with extreme-pressure additives and the like and a martensite structure is contained have a problem that there is a possibility that a sufficient sliding ability is not manifested under extremely low sliding speed (0.01 to 2 m/min), too.
In the sintered copper alloy material according to JP-B No. 6-6725 having self lubricity suitable for use on a ware plate or the like of a press machine, local metal contact with an opposite member tends to occur under sliding conditions in which a lubricating oil film is not easily formed due to extremely low sliding speed and high surface pressure, resultantly there is a problem that sufficient seizure resistance and wear resistance are not obtained easily. Further, there is also a problem that when the addition amount of soft solid lubricants such as graphite, MoS2 and the like dispersed in the sintered copper alloy material is over 2.5 wt %, its strength decreases remarkably.
In the above-mentioned wear resistant sintered alloy for oil-containing bearing according to JP-A No. 8-109450, the plastic deformation of a base is reduced and load applied on a base alloy in sliding contact state is decreased by dispersing a large amount of soft Cu particles in a martensite phase and dispersing alloy particles harder than the martensite in a base, however, it has a problem that an effect of improving adhesion resistance is not sufficient since co-existence of dispersion of soft Cu particles and dispersion (5 to 30 wt %) of hard alloy particles in one alloy is limited and load applied on the base alloy in sliding contact state is concentrated on its hard alloy particles. Further, there is also a problem that by addition of a large amount of alloy particles harder than a martensite in a base and having no self lubricity, a contact opposite material is remarkably attacked by adhesion wearing, and the temperature of a contact surface increases to easily cause a seizure phenomenon. Furthermore, there is a problem that a bearing bushing made of this wear resistant sintered alloy for oil-containing bearing as a constituent material is expensive. There is also an investigation of lowering cost, increasing a sliding ability, improving maintenance and the like by sharing the role of a sliding function to a cheap contact material constituting mutual slip pair, however, a solution is not attained yet.
The Cu—Al—Sn-based sintered contact material suggested in JP-A No. 2001-271129 which is a prior application of the applicant is an extremely excellent bearing material which can be used at extremely low sliding speed (0.6 m/min or less) and a high surface pressure of up to 1200 kgf/cm2, which cannot be attained by conventional bearing materials of iron-carbon alloy base, however, it has a problem that, due to somewhat lack in pressure resistance required in use environments in which earth and sand invade, wearing progresses easily under such use environments.
The sintered contact material according to JP-A NO. 7-1662778 has, when a lubricating function formed by Mo of 5% by area or less or Fe-55 to 70 wt % Mo (ferro-molybdenum phase) of 15% by area or less based on the contact area using a bronze alloy phase as a mother phase is singly performed, problems that, under extreme low sliding speed and high surface pressure conditions such as for the above-mentioned work implement connecting portion, formation of an adhesion portion by local metal contact with an opposite member is not sufficiently prevented and adhesion wearing progresses, and conformability resistance, seizure resistance and wear resistance are not sufficiently attained, and hard MoFe (ferro-molybdenum) particles remarkably attack a contact opposite material. It is easily envisaged to be able to improve a sliding property by regulating the addition amount of Mo at 5 wt % or more, however, there occurs, in this case, a new problem that the structure strength of the sintered contact material is decreased.
The high tensile brass-based and Al bronze-based contact materials containing a lead bronze-based material and lead according to JP-B No. 5-36486 and JP-A No. 5-214468 suitably used as a constituent material of a floating bushing in a turbo charger are recently required to improve seizure resistance and wear resistance under higher speed and higher temperature sliding and to manifest excellent seizure resistance, wear resistance and corrosion resistance even under poor lubrication condition in starting of a turbo charger and the like, however, these contact materials have a problem that (1) a Pb-lack layer after elution of Pb is formed near a contact surface (see, FIG. 22(a) to (c)), and (2) even after stop of operation of a turbo charger, the temperature at a bearing portion increases to high temperatures around 300° C. due to heat conduction from a turbine and consequently a layer of accumulation of CuS and sludge formed by reaction with S in a lubricating oil is formed on a trace of Pb connecting to the contact surface (see, FIG. 23(a) to (b)), therefore, a lubricating ability by Pb decreases, and essential improvement against seizure resistance and durability (elongation of life) is impossible. Further, from the standpoint of recent environmental problems, there is a problem that a large amount of Pb contained in a material is not preferable.
Regarding hydraulic pumps/motors, there is recently a tendency of increase in pressure and further decrease in size, therefore, improvement in seizure resistance and wear resistance is desired for sliding parts constituting the hydraulic pumps/motors, however, the conventional lead bronze, bronze and brass-based contact materials according to the above-mentioned literature (Japan Non-ferrous Metal Casting Association ed., “ENGINEERING DATA BOOK FOR COPPER BASED ALLOY CASTING”, Issued by Materials Process Technology Center (SOKEIZAI CENTER), Jul. 30, 1988, p. 134-155) have a problem that they are insufficient in strength, seizure resistance and wear resistance for higher output and further decrease in size.
The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide a thermal spray membrane contact material, contact member and contact part, and an apparatus to which they are applied, excellent in seizure resistance and wear resistance under extremely poor lubrication conditions such as high surface pressure and low speed sliding and swinging and the like, and excellent in conformability in sliding and showing excellent seizure resistance and wear resistance even under high speed and high temperature sliding and high surface pressure and high speed sliding.